Lizards, PowerPoint 1• Metaphorical statement:

– God must love lizards because she/he created an enormous number of them (including snakes)!

• Two conflicting tales of evolution:– Conventional for twenty years:

• Earliest lizards preserve ancient jaw/tongue structures• More advanced lizards move into a world of smells

– Radically new (and not [yet?] widely accepted): • Earliest lizards had lost ancient jaw/tongue structures• Movement into a world of smells begins very early• Manufacture of disabling toxins is early adaptation• “Iguanian” lizards are not primitive but are derived

The basic taxonomic question: Does the skull-kinesis plan define the

most fundamental within-lizards split, or is it primitive amongst

lizards?

• Tuataras and iguana-type lizards manipulate food with their tongues, which therefore can’t do many other things.

• If this task were assumed in part by lips & jaws, then the tongue could be released for other functions, such as “smelling.”

• Diagram at left shows a non-iguana-type mobile skull. Lizards w/this type of skull can use tongues to enter “the world of smells.”

• (Whenever it occurred, evolution of cranial kinesis– skull movement– was pre-requisite to the evolution of snakes’ swallowing adaptations.)

Partial Agreements about Lizards (1 of 4 slides)

• Iguanian Lizards: Today’s main subject, this group is set apart from other lizards. The iguanians include 3 Families of lizards that tend to be visually oriented, low-energy ambush predators. Their tongues are involved with food manipulation and are therefore not available for other purposes. In this iguanians are like tuataras, the closest living lizard-relatives. But is this condition preserved from ancient ancestors, or was it re-evolved high in the lizard phylogenetic tree?

• Other Lizards: A subject for later classes, non-iguanian lizards have highly mobile jaws, and therefore their tongues can be used for purposes other than food manipulation. (See next slide.) In the conventional taxonomy, these animals are called Scleroglossan (= “hard-tongued”) lizards. This group includes the snakes.– Gecko-types (a firm taxonomic group). These animals pursue a number of specialties

(especially nocturnal lifeways) and depart from many of the usual lizard themes.– “Autarchoglossan lizards.” (This may or may not be an inclusive and coherent group.)

To greater or lesser degree, these lizards use their tongues to gather chemical information. The group includes:

• Numerous Families of “typical” lizards• Four Families of (near-) legless wormlizards (amphisbaenians)• Numerous Families of snakes.

…agreements 2: Lizard evolution in the broader reptilian context.

• No single factor defines lizards, so their ancestry is difficult to trace in the fossil record.

• About 245-200MYBP, lizard ancestors diverged from the line that was to become the Archosauria (thecodonts, crocs, dinosaurs, pterosaurs, and birds).

• Lizards were not a particularly impressive Order during the earlier Ages of Reptiles, but over time they became the most successful reptilian group. (Why? See next slide.)

• Furthermore, all major present lineages were established before or during the Cretaceous (135-65MYBP).

• Cenozoic (post-dinosaur) radiation has been comparable to that of the perching birds, the other successful tetrapods.

…agreements 3: Lizard evolution in community-context (think insects).

• The radiations of the lizards should be understood within the context of the radiation of the arthropods– because that’s what what most lizards eat.

• Arthropods invade the land about contemporaneously with tetrapods, but their first major radiation awaits the Jurassic success of gymnosperm plants (pine trees, etc.).

• The triumph of the angiosperms (flowering plants) during the Cretaceous is accompanied by an enormous, additional diversification of arthropods.

• Arthropod radiations also feed on arthropod radiations…. • Among terrestrial vertebrates, only lizards were positioned

to exploit this abundance of potential animal-prey!

…agreements 4: The snakes-versus-lizards non-issue.

• Old-time taxonomists were overly concerned with distinguishing lizards from snakes:– General characteristics of Order Squamata (which, of course, fit snakes too):

• epidermal scales• transverse vent• paired intromittent organs• vertebrae usually open-ended toward front

– Characters of some lizards and no snakes:• four legs (but…)• external ear openings (but…)• moveable eyelids (but…)

– Characters of “all lizards” (except of the lizards commonly called snakes):• in combination, fused mandibles and traces of both girdles

• Nowadays all herpetologists recognize that snakes are deeply embedded within the lizard tree. In other words, taxonomically, snakes are lizards.

Dare I consider the classification of Squamates?

• Lizards are a highly complex group with some experts listing more than 30 Families. (We’ll treat almost two dozen groups in the next couple of PowerPoints, & we’ll consider snakes later.)

• Themes to look for on next 4 (complex) slides:– What is presented as the most basic type of lizard?– How similar is this most basic type to lizard’s closest

living relatives (tuataras)?– Where are the snakes placed?– How many types are presented as having ambiguous

affiliations?

Conventional classification of lizards

Next slide simplifies…

Conventional Classification:Simplified Version

• Iguania is sister to all other lizard groups (i.e., to the “scleroglossans”).

• Gekkota is sister to all other “scleroglossans” (i.e., to the “autarchoglossans”).

• “Autarchoglossans” are divided into (at least) skink-forms and anguid-forms (and others).

• Snakes, dibamids, and “wormlizards” form scleroglossan clades of uncertain affiliation, probably within the Autarchoglossa.

• Remember: Almost all these generalizations are now under question.

New Suggested Classification of Lizards

Suggested New Classification:Simplified version

Considering the Iguanians:our

first major lineage

• Are Iguanians the most ancient lizard type?• This lizard-plan is definitely a good one, for iguanians are

hugely successful around the world today.• The group includes 3 Families and about 1500 species.

General thoughts on Iguanian lifeways• Iguanian jaws & lips are not typically specialized, so the

tongue retains (regains?) its original manipulation-function, and iguanians emphasize vision instead of smell.

• Vision is appropriate for real-time detection of prey.– Iguanidae & Agamidae: detect the slightest motion….– Chamaeleonidae: detect distant prey….– (Of course there are iguanian exceptions to this visual emphasis.)

• Thus most iguanians are sit-and-wait predators, and…– Thus most iguanians can combine thermoregulation with hunting.– Many are heavy-bodied….– Most have low to medium metabolic rates….– Most emphasize burst-speed over endurance.– Many iguanians are highly cryptic.– Many iguanians are microhabitat specialists.– Many are territorial (next slide).

Typical iguanian territoriality

• Typically, females minimize territories, & males maximize territories. Why?– Male strategy: inseminate as

many females as possible. But what are the limiting factors?

– Female strategy: 1 good mating & put your energy into eggs (and/or into staying alive).

• Other mating systems:– Promiscuity– Monogamy– Dominance hierarchies

• Should mating-structures be maintained outside of the breeding season?

Next: Begin tour of Families…

Family Iguanidae

• About 50 genera with probably > 1000 species.

• Ranges will be shown when separate subfamilies are treated below. (These & other subfamilies might be promoted to Family level.)

• Small, medium, & large.• Often brightly colored

(especially males); often w/ crests, dewlaps, etc.

• Thermoregulators and thermal conformers.

• Mostly ambush predators.• Few-egg types & many-egg

types.• Tail usually long, usually

autonomous.Basiliscus plumifrons

Iguanidae: Crotaphytinae

• 2 genera, c. 12 species• Most are arid-land or rock-

outcrop specialists.• Feed on large arthropods or

other lizards.• All species are sexually

dimorphic, with males larger than females.

• Females develop orange or red spots when carrying eggs. (Why???)

Crotaphytus bicinctores

Iguanidae: Iguaninae

• 8 genera & c. 34 species• Iguanines are medium to

large in size.• Amblyrhynchus has salt

glands & eats marine algae in Galapagos.

• All other genera are hindgut cellulose fermenters.

• Some have unusual thermoregulation strategies.

• Most have highly developed sense of smell (for stuff of low molecular weight).Brachylophus fasciatus

Fiji Islands

Iguanidae: Oplurinae

• 2 genera & 7 species• Limited to Madagascar.• Small to medium-large

lizards mostly living in trees or rocks.

• Most have spiny tails.• All are thermophilic,

often seeking open sun.• During breeding season

males show bright colors & defend territories.

Chalarodon madagascariensis

Iguanidae: Phrynosomatinae

• 10 genera, c. 125 species• The subfamily is diverse.• Many are arid-habitat

specialists, and many are somewhat flattened.

• Thermoregulation is often precise.

• Many species are strongly sexually dichromatic.

• Phrynosoma (next slide) has weird defensive behaviors.

Sceloporus malaciticus

Phrynosomatinae (cont.): How lifestyle parameters

of horned lizards are linked together.

• They eat ants & little else.• Ants are small & chitin-covered, hard to digest; thus many

must be consumed & slowly processed.• So lizard must have large stomach/body ratio.• Large stomach dictates slow-moving body form.• So, lizard can’t outrun predators; camouflage & lie low.• So, lizard can’t thermoregulate well.• Since lizard doesn’t move much, she won’t have to carry

eggs around very far, so she produces lots of them. Etc.

Iguanidae: Polychrotinae (anoles)

• 2 or 11 genera, depending on whom you ask; > 440 species

• Usually sexually dichromatic, with males possessing bright, extendable throat-flaps (dewlaps).

• Most are arboreal; some converge w/chameleons, others w/geckos.

• Most eat insects; most are ambush predators or visual stalkers.

Anolis conspersus

Iguanidae “Tropidurinae”

• 9-12 genera and about 270 species

• Ecologically diverse, but:– Most are thermoregulators

(though rainforest types have difficulties…).

– Most rely on crypsis.– Most are ambush predators.

• Some forms are highly polygynous, with males breeding many females.

• In some species, dominant males are distinguished by coloration.

• The group is thought by some to be paraphyletic.

Plica plica

Three additional iguanid subfamilies(that I do not choose to discuss in any detail)

• Leiosaurinae:– 7 genera– South American– Many forest animals, most extremely cryptic

• Hoplocercinae:– Poorly known South American forest lizards.– 3 genera, about 12 species.

• Corytophaninae:– 3 genera, about 9 species.– Basiliscus is semi-aquatic.

Family Chamaeleontidae

• 4-6 genera, c. 130 species

• Highly specialized arboreal insectivores:– vertically flattened body

– prehensile tail

– zygodactylous feet

– turret eyes

– changeable color

– projectile tongue

• Often w/ornamentation, sometimes sexually dimorphic.

Chamaeleo calyptratus

Chamaeleontidae (Infraorder Iguania)

• Foraging techniques:– They move so slowly; are

they stalkers or ambush predators?

– When scanning, eyes send alternating images to brain @ about 1-second intervals.

– When ranging, eyes send simultaneous images; eyes enlarge image & find range by focusing.

• Demography:– Large investment in large

number of small offspring.

– Rather short lifespan.

Family Agamidae

• About 45 genera w/ about 300 species.

• Mostly diurnal; mostly drab (except some breeding males); social commo often by means of shape.

• Many are Old World iguanid cognates.

• Some highly structured, dense colonies.

• Some large herbivores.• Some ornamented.

Physignathus cocincinus

Agamidae (Infraorder Iguania)

• Agamids are medium to large in size.

• Legs are well developed.

• Many agamids are terrestrial, and the vast majority are diurnal.

• Except for the genus Phrynocephalus, all agamids lay eggs.

• Southeast Asia’s Draco (left) is an accomplished glider.

Draco volans

Here are other, more representative agamids.

• Note distinct shapes– vertical compression in arboreal species (left) and horizontal compression in terrestrial species (above).